In the semiconductor packaging fields, what is attracting attention as a connection form capable of meeting an increase in the pins of the device or high density packaging is not the conventional loop connection via wire bonding but is flip chip packaging technology which connects a semiconductor element directly to an electrode over a wiring substrate via a bump electrode formed on the electrode portion of a semiconductor chip.
When wire bonding is adopted, it is necessary to keep a connection area for electrode pad around the semiconductor chip mounted on a semiconductor device. With an increase in the number of pins, the area inevitably becomes larger.
According to the flip chip packaging technology, on the other hand, the connection can be completed within the area of a chip to be mounted. This makes it possible not only to decrease the packaging area but also to shorten the connection wiring length.
Moreover, since the circuit surface comes on the mounting side of the substrate, another semiconductor chip having at least an equal size can be stacked thereover. This technology can therefore be applied advantageously to a three-dimensional packaging structure which has attracted recent attentions.
As the flip chip packaging system, a system of having a solder bump at a chip electrode portion and achieving electrical conduction by solder connection has been popular. In order to satisfy the recent pin-pitch decreasing tendency, however, a system of disposing a gold bump on a chip electrode portion and achieving electrical conduction by gold bump connection has come to be employed frequently.
There are two connection methods using a gold bump. One is a so-called metallurgical bonding method such as gold/gold metal bonding or gold/solder connection obtained by applying a solder paste between a gold bump/substrate electrode. The other one is a non-metallurgical bonding method in which electrical conduction is achieved by the contact between a gold bump and a substrate electrode.
The metallurgical bonding method is generally excellent from the viewpoint of reliability at the bonded portion, but has a demerit, because it has a solder bonding step which needs high-temperature treatment.
The non-metallurgical bonding system is, on the other hand, presumed to be effective for actualizing future narrow-pitch connection, because the electrical conduction can be attained not only at low temperature but also in a convenient manner and at a low cost.
The non-metallurgical bonding system has thus the above-described advantages. On the other hand, it involves the demerit that since it adopts contact conduction, connection reliability is not stable if design or material selection is not proper. At present, therefore, this system has not yet been applied to products generally.
There is a description on the improvement in connection reliability in the non-metallurgical bonding system, for example, in the inventions disclosed in Patent Document 1 and Patent Document 2. In these Patent Documents 1 and 2, disclosed is a connection structure in which an elastic modulus of an insulating surface layer of a substrate has been adjusted appropriately in order to obtain a uniform contact state between a bump electrode disposed on a semiconductor chip and an electrode formed on a packaging substrate.    [Patent Document 1] Japanese Patent Laid-Open No. H9(1997)-199468    [Patent Document 2] Japanese Patent Laid-Open No. H10(1998)-245615
There is a demand for a further decrease in the pitch between electrodes in order to meet the request for imparting semiconductor devices with more functions and for decreasing the size of them.
In order to narrow the pitch between electrodes in the non-metallurgical bonding system, a problem how to stabilize the contact state between a bump electrode and a substrate electrode must be resolved.
As the miniaturization of bump electrodes proceeds in future with the pitch narrowing tendency, when an adhesive material (non-conductive or anisotropic conductive resin) for sealing the surroundings of a bump has a large linear expansion coefficient, for example, plastic deformation of a bump electrode is accelerated upon thermal contact bonding by the thermal shrinkage of the adhesive material, leading to an inconvenience such as easy separation of the contact surface or disconnection upon re-heating.
On the contrary, when the linear expansion coefficient of the adhesive material is small, a certain contact pressure cannot be obtained stably when the surface layer of the packaging substrate has low rigidity (elastic modulus). This also leads to an inconvenience such as easy separation of the contact surface or disconnection.
Only by adjusting the rigidity (elastic modulus) of an insulating material constituting the surface layer of the packaging substrate as in the technology described in the above-described Patent Documents 1 and 2, it is difficult to keep high reliability of the non-metallurgical flip chip connection corresponding to narrow pitch connection.
Moreover, misalignment of a bump electrode and a substrate electrode upon mounting, which has not been taken up seriously as a problem in the background art, will become a problem under pitch narrowing tendency in future. When the pitch becomes narrower, a 10 to 15 μm misalignment of the mounting position of a bump relative to a substrate electrode will decrease a contact conduction region by almost half. This tendency becomes conspicuous as the pitch becomes narrower.
When an actual mass production process of a semiconductor device is taken into consideration, it is essential to avoid an influence of misalignment of the bump electrode on the connection yield (fabrication yield) even if existence of such a level of misalignment is permitted.
For actualizing the connection of electrodes with a narrow pitch, miniaturization of interconnect patterns around a substrate electrode is inevitable so that the wiring strength of a substrate reduces radically owing to the generation of a thermal stress.
Accordingly, when the reliability of the whole package structure in a semiconductor device is considered, it is essential to actualize a substrate constitution capable of ensuring not only connection reliability of the contact conduction portion of a bump electrode but also connection reliability of minute interconnects over the substrate.